192 THE ROYAL SOCIETY OF CANADA 



any gaseous contamination introduced into the helium in the working 

 of the cycle may be removed. Provision is being made for indicating 

 the level of the liquid hydrogen in the refrigerator by means of two 

 constant volume helium thermometers with bulbs M and M^. These 

 bulbs are made of German silver and are to be connected to glass 

 manometers by means of steel capillary tubing. The valve V, with 

 its spindle C\ both pre-cooled with gaseous hydrogen, will enable one 

 to regulate the supply of liquid hydrogen. The flask E that is to be 

 used for storing a reserve supply of liquid hydrogen is not to be silvered 

 and is to be kept immersed in a flask F^ filled with liquid air. This 

 latter flask is to be provided with two unsilvered observation strips 

 on either side to enable one to see the level of the liquid hydrogen 

 directly. Provision is also made in the design for siphoning liquid 

 hydrogen from the store bottles into the reserve flask Fi and since the 

 vapourized hydrogen will necessarily be almost absolutely pure, 

 provision has been made in the apparatus for carefully collecting and 

 storing it. 



The helium, as it is condensed on liquefaction, will collect in the 

 bottom of the silvered flask Fz that is to be made with a specially 

 designed delivery tube P. This tube will be double walled and silvered 

 in the same manner as an ordinary vacuum flask. In this way it 

 will be possible to transfer the liquid helium to the flask F^ or to any 

 other suitable apparatus in which it may be required. In the design 

 of the apparatus every precaution has been taken to prevent loss of 

 helium or its contamination with hydrogen. 



8. Summary 



In the statement above there are set forth the underlying prin- 

 ciples, the design and many details as well of the equipment that 

 will soon be completely installed in the Physical Laboratory of the 

 University of Toronto for the purpose of liquefying hydrogen and 

 helium. 



Note. — While presenting this paper I desire to take the oppor- 

 tunity of acknowledging my very great indebtedness to Professor 

 Kammerlingh Onnes of the University of Leiden, Holland. 



The hydrogen purifier and liquéfier, as well as the helium liquéfier, 

 were designed in accordance with drawings furnished to me by him. 

 I also had the benefit of his advice in working out the details of the 

 hydrogen compressor. 



